This invention relates generally to seat assemblies and more particularly to seat assemblies for automobiles and the like that comprise a trim cover and a foam cushion commonly referred to as a bun.
In the past, trim covers, particularly cut and sewn type trim covers, have been attached to foam cushions-by hook and loop fasteners, also known as Velcro fasteners. In these known constructions, the foam cushions generally have a central seating portion defined by elongated recesses. Strips of hook fasteners are secured to the bottoms of these elongated recesses by adhesives or insert molding operations so that the hooks extend up into the elongated recesses. The trim covers, on the other hand, have strips of loop fasteners secured to their bottom or inside surfaces. In the case of cut and sewn type trim covers, the strips are secured to the salvage ends that are formed when abutting side edges of adjacent panels are sewn together. In any event, the trim cover is attached to the foam cushion by aligning the strips of loop fasteners on the bottom of the trim cover with the strips of hook fasteners in the recesses of the foam cushion and then pressing the trim cover in place so that the loop and hook fasteners interlock. An example of such a system is disclosed in U.S. Ser. No. 07/859,791 filed Mar. 30, 1992 and assigned to General Motors Corporation.
This hook and loop fastener system works well. However, it is a relatively expensive process for several reasons including the cost of the fasteners themselves, the cost of attaching the fasteners to the trim cover and the foam cushion and the cost of engaging the cooperating fasteners to each other, which is essentially a manual operation.
U.S. Pat. No. 4,692,199 granted to Eric F. Kozlowski and Edmund R. Kruger on Sep. 8, 1987 discloses another method of attaching trim covers to foam cushions. In this method, a vacuum is applied to a porous contoured mold to draw an impervious adhesive film against a fabric or cloth trim cover to conform the trim cover to the contours of the mold surface. A foam cushion is then pressed against the adhesive film and the trim cover while heated fluid is passed through the porous mold and the fabric trim cover to diffuse the adhesive film into the trim cover and the foam cushion and thus bond the trim cover to the foam cushion. A second vacuum is then applied through the foam cushion to remove moisture residue resulting from the steam and to cool and cure the adhesive.
This method has several drawbacks. A major drawback is that this method requires passing heated fluid, such as steam, through a porous fabric trim cover to bond the foam bun to the trim cover. Because of this heating requirement, the process and the tooling for the process are relatively expensive; the trim cover and any backing are susceptible to shrinkage and delamination, and the nap of fabric trim covers can be distorted limiting the types of fabric that can be applied with the process. Another drawback is that this method does not tolerate dimensional variations very well and consequently tight tolerances for the trim cover and the foam bun are required. Another drawback is that the method is very sensitive to the surface characteristics of the foam bun or cushion.
There is also another drawback when the process is used in making a sculptured seat having a cut and sewn trim cover applied to a foam bun having deep styling grooves. The process often requires plastic locating strips sewn in the style line seams that are formed when adjacent panels of the trim cover are sewn together. These plastic strips are needed to register the style line seams with style line grooves in the foam bun. These plastic strips add further material and manufacturing cost. The plastic strips are also a possible source of discomfort to the seat occupant because remnants beneath the stitching remain in the finished seat.
U.S. Pat. No. 5,005,805 granted to Michael E. Lowe on Mar. 19, 1991 discloses yet another method of attaching permeable fabric trim covers to foam cushions. In this method, a sheet of polyolefin film is positioned on one side of a permeable fabric or cloth trim cover to form a composite that is vacuum drawn against a vacuum forming tool fixture to conform the composite to a shaped surface of the tool fixture. A foam cushion having an adhesive layer applied to a shaped surface is then pressed against the composite while steam heat is applied to the tool fixture to deteriorate the polyolefin film and allow the adhesive layer to bond the foam cushion to the fabric trim cover.
This method also has several drawbacks that are more or less the same as those discussed above. One more or less common drawback is that this method also requires passing heated fluid, such as steam, through a porous fabric trim cover to bond the foam bun to the trim cover. This heating requirement has the same adverse effects noted above, namely, the process and the tooling for the process are relatively expensive; the trim cover and any backing are susceptible to shrinkage and delamination; and the nap of fabric trim covers can be distorted, limiting the types of fabric that can be applied with the process.
Another common drawback is that this method does not tolerate dimensional variations very well either, and consequently tight tolerances for the trim cover and the foam bun are still required. Moreover, this process still requires plastic locating strips sewn in the style line seams of the trim cover to register the style line seams with style line grooves in the foam bun in some instances. These plastic strips add further material and manufacturing cost and a possible source of discomfort to the seat occupant as noted above.